This article examines Customary Law and the Formal Legal System: Complementarity, Conflict, and Reform in East Africa: Post-CPA and Beyond with a focused emphasis on Tanzania within the field of Political Science. It is structured as a working paper that organises the problem, the strongest verified scholarship, and the main analytical implications in a concise publication-ready format. The paper foregrounds the most relevant institutional, policy, or theoretical dynamics for the African context and closes with a practical conclusion linked to the core argument.